Power amplifier



FIG. 1 is a perspective view of the power amplifier embodying my new design;

FIG. 2 is a left side elevation view thereof, the right side being a mirror image of the side shown;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a front elevation view thereof;

FIG. 5 is a top plan view thereof; and

FIG. 6 is a bottom plan view thereof. 

The ornamental design for a power amplifier, substantially as shown and described. 